Electrical discharge apparatus for forming



June 1965 R. J. SCHWINGHAMER 3,188,844

ELECTRICAL DISCHARGE APPARATUS FOR FORMING Filed Jan. 17, 1962TRIGGERING 84 SWITCH POWER SUPPLY so 75 L82 FIG. 2

H INVENTOR.

B ROBERT J. SCHWINGHAMER FIG. 3

A T TORNE Y5 United States Patent {The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payrnent of any royaltiesthereon or therefor.

This invention relates to high energy rate forming and more particularlyto an electrical discharge apparatus for high energy rate forming.

Recent trends in manufacturing for formed metal parts in large sizes andformed metal parts having complex configurations have led to thedevelopment of high energy rate forming techniques which provide aninstantaneous force for forming which would be impractical byconventional machinery such as the hydraulic forging press and drophammer. These high energy rate forming techniques generally involve theuse of chemical compounds which are exploded under water whereby shockwaves are generated vand transmitted by the water against a metal blank.Chemical explosives do not, however, provide for rapid and uniformrepeatability and are often hazardous to handle and store.

The explosive-like energy release of a rapid discharge ofelectrostatically stored energy between two electrodes has also beensatisfactorily utilized to a limited extent for high energy rateforming. The placing of a high electrical potential of severalkil-ovolts between two electrodes located under water results in acurrent flow which first vaporizes the water in the vicinity of theelectrodes and then causes the vapor to become highly dissociated andionized. This ionized vapor is a highly conductive path and permits atremendous electrical current discharge between the two electrodes with:a corresponding intense pressure or shock wave that radiates radiallyfrom the conductive path and is transmitted by the water. However, aconsiderable amount of current is necessary before the ionized vapor isformed which means less useful work and somewhat unpredictable resultsfrom one electrical discharge to another. Also, the explosive path ofthe electrical discharge could not be shaped to obtain the versatilityof chemical explosive charges which by having a cylinder, cord, or sheetshape could obtain an energy release pattern which would tend to apply aforming force exactly where needed.

Accordingly, it is an object of this invention to provide a highlyeflicient electrical discharge apparatus which rapidly and repeatedlyobtains energy releases in a particular direction.

A further object is to provide an electrical discharge apparatus whichwill release and control sufficient energy to efiiciently formmaterials.

Other and further objects, uses, and advantages of the present inventionwill become apparent as the description proceeds.

In accordance with this invention an electrical discharge apparatus isconstructed having a blast head with a coneshaped chamber and a dieblock in cooperative relationship thereto which has a forming cavityaligned with the chamber. A metal blank which is adapted to be formedseparates the chamber from the forming cavity.

Within the chamber and adjacent the apex thereof are two spacedelectrodes having a metal wire bridged there- 7 between which has aV-shaped portion converging away from the apex of the blast chamber.-Also, within the blast chamber is a pressure transmitting liquid.

The two electrodes are electrically connected to a condenser bankthrough a suitable triggering switch. When the condenser bank isdischarged through the electrodes and wire, the wire explodes andgenerates a shock wave which is transmitted by the liquid toward theblank. The electrical circuit and wire parameters are selected whereby acurrent pause or dunkelpause does not occur.

This will be more readily understood by the following detaileddescription when taken together with the accompanying drawings, inwhich:

FIGURE 1 is a perspective view of an apparatus for electrical dischargeforming.

FIGURE 2 is an elevation cross-sectional view taken along line 2-2 ofFIGURE 1, showing some parts in full, and including an electricalschematic wiring diagram.

FIGURE 3 is a partial elevation cross-sectional view showing theelectrode and wire relationship for the apparatus of FIGURE 1.

Referring now to the drawings, there is shown in FIG- URES 1 and 2 anapparatus 11 for electrical discharge forming having a die block 13 witha forming cavity 15 and a bore 1-7 communicating with the cavity 15. Ametal blank 19 rests upon the upper surface 21 of the die block 13 andcovers the forming cavity 15. The blank .19 has a hold-down ring 23 uponits upper surface 25 to frictionally hold it in position. A blast head27 with an inner cone-shaped chamber 29 converging from an opening inits base surface 31 is situated upon the upper annular surface of thehold-down ring 23. The forming cavity 15 of the die block 13, theaperture 33 of the hold-down ring 23, and the conical chamber 29 of theblast head 27 are in an aligned relationship. As shown best in FIGURE 2,cap screws 35 extend through lugs 37 integral with the blast head 27 andon through the holddown ring 23 near its outer periphery, and intothreaded bores 39 within the die block 13.

The blast head 27 has a dielectric material portion 41 which forms theregion adjacent the apex of the chamber 29 and extends to the uppersurface 43 of the blast head 27. The dielectric material portion 41 hasa peripheral flange 45 resting upon an annular shoulder 47 of the blasthead 27 to prevent it from slipping down into the chamber 29. A pressureplate 49 is secured by a series of cap screws 51 to the upper surface 43of the head 27 to prevent the dielectric material portion 41 from beingblown out by an electrical discharge within the chamber 29 as describedhereinafter.

Extending through the dielectric material portion 41 are two spacedelectrodes 53 and 55 having inner bent portions 57 and 59, respectively,directed in an opposed manner into the chamber 29 adjacent its apex. Ametal wire 61 having a centrally located V-shaped portion is fixed byits opposite ends to the opposed bent portions 57 and 59 of theelectrodes 53 and 55, respectively. This is accomplished as shown inFIGURE 3 by placing each end of the wire 61 into a bore 63 providedwithin each of the bent portions 57 and 59 and securing it by a setscrew 65. The wire 61 is positioned whereby its V-shaped portionconverges in the diverging direction of the chamber 29 and points towardthe metal blank 19.

The pressure plate 49 has a centrally located boss 67 upon its uppersurface and an opening 69 which extends through the boss 67 and plate49, A coaxial transmission line 71 extends through the opening 69 and isheld therein by a collet chuck 73 which fits tightly about the line 71and is in threaded contact with the boss 67.

The coaxial transmission line 71 is electrically connected to theelectrodes 53 and 55 by attaching its core conductor 75'to electrode 55and its shield conductor- '77 to the. other electrode 53. The electricalconductors 75 and 77 are also attached to a high energy electricalstorage bank 78, which is illustrated in FIGURE 2 as a series ofparallel related capacitors 89 having a power supply 82 to charge themtotheir high electrical potential.

A suitable triggering switch 84 is provided in the electrical conductor77 for discharging at the proper; moment the capacitors'80 through theelectrodes 53 and 55 and wire 61 whereby the wire 61 willbe vaporizedwith explosive violence. I

The chamber 29 is filled with liquid 85, water'for example, fortransmitting the shock wave generated by the explodin'g wire 61againstthe metal blank 19 s'othat it will be formed against the diecavity 15.

The metal blank 19, although tightly held between the 'dieblock .13 andthe hold-down ring 23, is able to slip slightly when being forced intothe forming cavity 15. This.,slight. slippage prevents the blank 10from.

'ful wouldbe encompassed within the conical volume defined bythe metalblank 19 and thewire 61. The rest of the energy distribution outside ofthis conical volume would'have been lost from performing useful work.

For efficient operation, the parameters of the metal wire 61 and itselecterical circuit should be selected by known criteria whereby acurrent pause or dunkelpause will not occur and whereby the capacitors80 are com pletely discharged. approximately instantaneously with r theexploding of-the wire 61. It is also preferred if the included angle ofthe V-shaped portion of the wire 61 has an angle between 50: and 70degrees and the included cone angleof the chamber 29 has an angle ofapproximately 55 degrees.

It is apparent that an electrical discharge system utilizing a bentbridge wire has been disclosed which is instrumental in: concentratingthe explosive force of an electrical discharge" and this systemhas beenincorporated A directional shock wave is generated by the explodingjwire 61 because it is bent into'a V-shape.

bring itself into a state of equilibrium. When the current path is bent,as would result in using the V-shaped- 'wire 61, the magnetic flux inthe acute angle region of the bentpath, region A in FIGURE 3, would havea high density due to its concentration in a. region of smallerdimensions, and, correspondingly, the magnetic This is believed to bedueto the magnetic flux which normally surrounds an electrical currentpath and which tcndsto flux in the obtuse angle region, regionB inFIGURE 3, 7

would have a low density due to its spreading out'in a region of greaterdimensions. Accordingly, a situation occurs in the region of the bentcurrent path which results in a preferential motion of particles ofmatter away from the high densitymagnetic flux toward the low densitymagnetic flux in anefiort .to bring about a state I of equilibrium. Itis this preferentialmotion which is believed to result in the shapedshock wave generated by an electrical discharge through a V-shaped pathbe,

'ingfdirected in the converging direction of that path.'

. The shock wave generated by exploding the. wire 61 has substantiallythe same V-shape as the wire so that when the shock wave moves outwardlyfrom the vaporized wire 61 its apex strikes against the middle region,of the metal blank 19. This is. advantageous because the forming of themiddle portion of/thev metal blank 19 first will result in a'moreuniform wallthickness-to the finished blank 19 and more efficientforming. Otherwise, if the apex of the shock wave front first came 7against the metal blank 19 adjacent its outer periphery and formed thatportion against the cavity ISf-and then started forming the middleportion, the blank'19 would have been prevented'from slipping properly.'Improper slipping of the metal blank 19 may cause a rupture, non uniformwall thickness, and decrease in efiiciency of the" volume condition fordeforming a metal blank 29, and

with the explosion occurring adjacent the apex of the chamber 29, theshock wave is driven toward thediverging direction 'of the chamber 29without appreciable loss of energy. If, for example, the wire '61exploded in an unconfined medium, only that portion of there sultingspherical energy distribution which would be useinto an apparatus whichtakes full-advantage of the di rectional. sense of the electricaldischarge by bringing the explosive force generated thereby against ametal blank with high efliciency. Obviously,; many modifications andvariations of th present invention are possible in the light of theabove teachings. It is, therefore, to be understood that within thescope of the appended claims the invention may be Whatis claimed 'is: VV I '1. In. combination with a die having a forming cavity adapted to becovered by a restrained blank:

(a), means for directing a shockwave having a substantially V-shapedfront toward the center of said forming cavity wherebythe point of saidshock wave will strike the middle portion of said blank to form saidblank from its center outwardly;

(b) said means including: V

(l)- a blast head having an inner cone-shaped chamber converging from anopening in the peripheral surface thereof; a

' "(2) said blast head joining said die with said opening being alignedwith said cavity;

(3) two spaced electrodes supported by said blast head and extendinginto said chamber adjacent the apex thereof;

(4) a 'wire having a V-shaped portion substantially aligned with thecenter of said cavity and fixed to'and extending between saidelectrodes, and 1 .(5') said V-shaped portion converging away from saidapex of said chamber.

2. In an apparatus for forming metal blanks:

(a) a blast head having a base surface'adapted to rest .upon' thesurface of a die'block having a forming cavity; a a Y (b)- said blasthead having an inner cone-shaped chamber converging from an opening insaid base surface, saidopening adapted to be aligned with the formingcavity of said die'block;

(c) two spaced electrodes supportedby said blast head and extending intosaid chamber adjacent the apex thereof; V a.

(d) a wire having a V-shaped-portion;

(e) said wire being fixed to and extending between said electrodes andhaving its V-shaped'portion converging in the diverging direction ;ofsaid chamber and pointing toward the center of the opening in said blasthead; J a V l (f) said wire being adapted to'vaporize with explosiveviolence upon the placing of a high electrical potential between saidelectrodes so as to cause a shock wave having a -V-shaped frontdiverging toward the opening in said blast head and pointing toward thecenter of the opening in said blast head whereby a metal blank adaptedto be placed over the forming practiced other thanas specificallydescribed.

6 cavity of the die block will be formed from its center ReferencesCited by the Examiner mtwardly; FOREIGN PATENTS (g) said cone-shapedchamber of said blast head being adapted to drive the shock wave towardthe opening 119,435 3/58 Russla' of said blast head Without appreciableloss of energy; OTHER REFERENCES and Sha e Fasten En rave Test MaterialsW1th EX 10- (h) means mcludmg Swltch for supplymg a hlgh elec' sives lvlaterials in D esign Engineering February 1559 trical potential to saidelectrodes so as to cause said 2 pages 8 87. Wire to explode at adesired instant; (i) said means and said Wire having parameters 10WILLIAM J. STEPHENSON, Primary Examiner.

selected whereby a current pause or dunkelpause NEDWIN BERGER Examinendoes not occur.

1. IN COMBINATION WITH A DIE HAVING A FORMING CAVITY ADAPTED TO BECOVERED BY A RESTRAINED BLANK: (A) MEANS FOR DIRECTING A SHOCK WAVEHAVING A SUBSTANTIALLY V-SHAPED FRONT TOWARD THE CENTER OF SAID FORMINGCAVITY WHEREBY THE POINT OF SAID SHOCK WAVE WILL STRIKE THE MIDDLEPORTION OF SAID BLANK TO FORM SAID BLANK FROM ITS CENTER OUTWARDLY; (B)SAID MEANS INCLUDING (1) A BLAST HEAD HAVING AN INNER CONE-SHAPEDCHAMBER CONVERGING FROM AN OPENING IN THE PERIPHERAL SURFACE THEREOF;(2) SAID BLAST HEAD JOINING SAID DIE WITH SAID OPENING BEING ALIGNEDWITH SAID CAVITY; (3) TWO SPACED ELECTRODES SUPPORTED BY SAID BLAST HEADAND EXTENDING INTO SAID CHAMBER ADJACENT THE APEX THEREOF;